A. Field of the Invention
The present invention relates to a microphone system for collecting audio signals in an apparatus such as an audio recording/reproducing system, and more particularly to a directivity controlling apparatus of a microphone system and a method for controlling the same.
B. Description of the Prior Art
A microphone system for collecting to record audio signals has been suggested by systems of, as shown in FIGS. 1A to 1D, non-directivity having the same sensitivity with respect to the omni-direction of the microphone, single directivity having sensitivity concentrated in the slightly wide direction with respect to the front area of the microphone, super directivity having sensitivity concentrated in the extremely narrow front area of the microphone and periphery directivity having sensitivity concentrated in the right and left sides of the microphone.
FIG. 2 is a view showing a conventionally general mono audio processing system, which utilizes the non-directional, single directional, super directional or periphery directional microphone.
Audio signals respectively collected via a plurality of microphones 21a, 21b and 21c are mixed in an adder 23 via respective amplifiers 22a, 22b and 22c. A single monophonic audio signal provided from adder 23 is gain-controlled in an AGC circuit 24a and modulated by a predetermined frequency in a modulating circuit 24b of an audio signal processing part 24 to be provided to a recording system at the succeeding stage.
FIG. 3 is a view showing a conventionally general stereo audio processing system, in which an audio signal of a left channel L and an audio signal of a right channel R are received into respective microphones 31a and 31b to be amplified in respective amplifiers 32a and 32b. Then, the amplified signals are supplied into an audio signal processing part 33. At this time, audio signal processing part 33 has a first AGC circuit 34a and a first modulating circuit 34b for processing the audio signal of left channel L, and a second AGC circuit 34c and a second modulating circuit 34d for processing the audio signal of right channel R, thereby executing the audio signal processing upon respective channels. Thereafter, the signal from first modulating circuit 34b and signal from second modulating circuit 34d are provided to an adder 35e. Thus, adder 35e provides a L/R mixed stereo audio signal.
Referring to FIG. 4, audio signals depending on respective directivities of a middle microphone 41a and a side microphone 41b respectively having the single directivity and periphery directivity are collected. The collected audio signals are then amplified in respective amplifiers 42a and 42b, and added in an adder 42c to be supplied into an audio signal processing part 43.
Audio signal processing part 43 performs the automatic gain controlling and modulating processing upon a middle/side audio signal supplied from adder 42c both in an AGC circuit 43a and a modulating circuit 43b with respect to the first channel and in an AGC circuit 43c and a modulating circuit 43d with respect to the second channel, thereby providing a middle/side stereo signal obtained by being added in an adder 43e.
The conventional directional microphone system is categorized into the non-directivity, single directivity, super directivity and periphery directivity. A desired directivity effect can be obtained only by using a microphone(s) having a specific directivity.
Also, in case of using the directional microphone, the directivity is shifted according to the user's selection, and this is a cumbersome process. Moreover, this process induces the problems of impairing the collected audio signals resulting from unsuitable timing of the shift and impeding the recording of desired audio signals when recording the collected audio signals.
In particular, although the stereo microphone has the directivity shaped like a letter "V," the directivity with respect to the direction can be secured by the amplification level of the same magnitude based on a typical, preset gain value, i.e., just by the simple amplification of the received signals solely depending on the microphone directivity regardless of the magnitude of the input signal (input sound).